The present invention relates to coupling means for coupling of laser radiation into a monomode optical fiber of polarization-maintaining type.
Optical fibers of this special type are required, for example, in order to provide a flexible connection between an interferometer and the laser generator used to supply it. For such uses, it is extremely important to eliminate disturbing light of undefined condition of polarization since such disturbing light not only reduces the contrast of measurement signals but can, in the event of back-scattering along the optical axis, also adversely influence the control means of a laser generator wherein, for length-measurement purposes, frequency must be maintained stable to 1.sup.-7.
From European Pat. No. B1-0,031,274, it is known, in the case of annular interferometers of the Sagnac type, to bevel the ends of monomode fibers into which the laser beam is coupled. But said patent gives no further information with regard to the development of the coupling means.
Federal Republic of Germany No C2-2,723,972 describes a monomode-fiber coupling element which employs a transparent capillary. In that case, however, the capillary within which the fiber is eccentrically bonded, serves only as a holding element. No information as to coupling factor or freedom from disturbing light can be noted from said patent.
Federal Republic of Germany No. A1-3,431,996 describes a sensor in the form of an optical fiber having a beveled end contained in a transparent mount. The end surfaces of the fiber and mount are, however mirror surfaces, with the exception of the cross section of the core, so as to utilize light-impingement outside the core to obtain a reference signal. Aside from the fact that this fiber is not a monomode fiber of the polarization-maintaining type (and thus, if only for this reason, is unsuitable for supplying interferometers), a relatively high level of scattered light is present as a result of mirror action at the end surface.